The objective of this project is to gain an understanding, using the cat as a model system, of the anatomical substrates underlying extrastriate cortical visual mechanisms. This objective is being approached with electrophysiological mapping techniques and anatomical tracer methods. Anterograde and retrograde tracer methods are being employed to analyze the interconnections between the cat's extrastriate visual areas, as well as interconnections between selected visual areas and the visual zones of the lateral posterior complex ("pulvinar"). Present emphasis is being placed upon the ultrastructural organization of the thalamic zones which serve to interconnect cortical visual areas, and upon characterizing the relay cell populations of these zones with dual-retrograde labeling methods.